1. Field of the Invention
The present invention relates to a radiation imaging apparatus that uses a radiation detection panel of converting radiation ray to an electronic signal corresponding to the intensity of the radiation ray.
2. Description of the Related Art
A digital radiation imaging apparatus has been recently realized, where it directly digitalizes a radiation image by using so called a flat panel detector (FPD), a radiation detection panel, which is formed by closely contacting a phosphor and a solid-state image sensor having a large emitting area. Most analog radiation imaging apparatus on the market has been replaced by digital radiation imaging apparatus, which have been broadly used on the market. By using the digital radiation imaging apparatus equipped with the FPD, digital information can be instantly obtained from the radiation image, which reduces the workload related to image capture for operators and increases the efficiency of interpretation by medical doctors among many other advantages. Owing to technical progress, the digital radiation imaging apparatus is miniaturized to the size of a conventional analog cassette, and a portable digital radiation imaging apparatus, so called an electronic cassette, has been developed. The electronic cassette is superior to portability as well as the conventional analog cassette, and it has advantage such that it can be used for multipurpose by taking it along in a hospital ward.
In cases of portable image capture, because the weight of the subject to be imaged is often placed upon the image capture apparatus case, the image capture apparatus requires a high-strength structure in order to protect the radiation detection panel within it, which is made of thin, brittle glass, from the weight. Thus, the electronic cassette is desirable to have large rigidness and light weight.
On the other hand, the radiation detection panel has characteristic change by long usage and property of inducing low S/N ratio by a dark current. Japanese Patent Laid-Open No. 2002-040144 has proposed the apparatus having a light source to irradiate light for calibration of each element of the radiation detection panel. In this patent Laid-Open discloses a LED, an EL (Electronic Luminescence), a cold-cathode tube and a semi-conductor tube as such light source.
Japanese Patent Laid-Open No. 2007-163216 shows a configuration of placing a light source composed of a cold-cathode tube and a light guide panel on the low side of the radiation detection panel. Further, support members for the light source are placed on the low side of the radiation detection panel and the light source.
Because a light source of electronic cassette is desirable to be a light source without a light guide panel which stands in the way of the thinness and light weight, an EL light source is well suited to the light source, which is thin and lightweight and a planar emitter. On the other hand, generally speaking, a light emission amount of a light source including an EL light source, will have degradation if it is used for a long time. In medical field, a long durable years period for usage is desired comparing to that of general commercial products. For this reason, the exchangeability to parts having a short life is desired. Further, in actual medical site, immediate correspondence to a sudden failure of apparatus, and recovery of the apparatus are required.
Thus, a light source which has a life shorter than a life of radiation detection panel is desired to be exchangeable. However, in the prior art, it was difficult to exchange a light source because it needs to be placed between the radiation detection panel and the support structure of the radiation detection panel. Further, regarding the exchange work, the structure did not consider the workability.